Modern motor vehicles make use of driver assistance systems, which detect a lane boundary, such as a median or shoulder, by means of a camera arranged on the vehicle, and warn the driver if the vehicle gets critically close to the edge of the lane or even drives over it. These assistance systems experience difficulty in performing their task when the lane boundary is missing, fragmented or very dirty, or when temporary and permanent lane markings are present simultaneously (e.g., in a construction zone) and only the temporary lane markings are to be considered.
US 2009/0125204 A1 described a driver assistance system in which a vehicle here referred to as an ego or first vehicle combines and evaluates the information of a lane detection system and information from a camera that acquires an image of the lead vehicles, so as to influence the steering of the first vehicle based on the combined information.
It is logical for the first vehicle to orient itself toward a vehicle ahead of the first vehicle, since its driver and/or assistance systems can better recognize the lane boundaries on a road segment ahead than the first vehicle or its driver, and hence have a head start over the latter in terms of recognition. If a vehicle ahead, referred to herein as the second or lead vehicle is driving “correctly” in that it keeps a reasonable distance from the lane boundaries and maintains a reasonable speed reflecting the curve radii of the lane, the first vehicle is also driving correctly when it follows the route of the lead vehicle at the same speed. However, there is no guarantee in practice that the lead vehicle is driving correctly, and errors or inaccuracies in evaluating the images delivered by the camera can also result in deviations between the actual position of the lead vehicle and the position acquired by the first vehicle. The further the distance between the ego vehicle and the vehicle ahead, the greater such errors become. Therefore, the greater the head start of the lead vehicle in terms of recognition, the less useful it becomes. Poor visibility conditions such as those produced by a darkly reflective, rainy road can detract from the detection of both the lead vehicle and the lane boundaries. It is precisely in critical situations where there is no visual contact, e.g., when a lead vehicle has disappeared behind a curve, that the conventional method yields no usable information. As a consequence, it does not make sense for the first vehicle to be excessively oriented toward the path traveled by the lead vehicle.